Method of flocculating solids



United States Patent 3,414,512 METHOD OF FLOCCULATING SOLIDS Tegner A. Johnson, Grand Rapids, Minn., assignor to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Nov. 30, 1966, Ser. No. 597,898 2 Claims. (Cl. 210-51) ABSTRACT OF THE DISCLOSURE Many ore concentrating processes involve the use of large quantities of water. Before such water can be reused in the process or drained into streams or lakes, it may be necessary to settle out suspended solids. A common flocculating agent for hastening settling of the solids is a combination of caustic soda and starch. This floc- SPECIFICATION This invention relates to an improved method of flocculating solids suspended in water.

My flocculating method is especially applicable to slimes or tailings which remain suspended in water after an ore concentrating operation, particularly iron ore. Before such water can be re-used or even drained into streams or lakes, it is usually necessary to settle out most of the suspended solids. Numerous flocculating agents are known for hastening the settling. One such agent which has been used successfully is a caustic starch, a combination of starch and sodium hydroxide. However, caustic starch is ineffective as a flocculent when used with surface drainage water from certain sources, for example the St. Louis River in Minnesota. I am not fully aware of the explanation for its ineffectiveness in these waters, but I believe it is due to the presence of impurities, such as organic matter, oxygen or acidity-controlling salts, in trace amounts.

An object of my invention is to provide an improved flocculating method in which I use a caustic starch flocculent effectively with surface drainage water.

A more specific object is to provide a flocculating method in which MgSO MnSO and Ca(OH) are added to surface drainage water to counteract the flocculationinhibiting effect, whereby a caustic-starch flocculent becomes effective.

According to my invention, I add to surface drainage water a combination of reagents as follows:

Pounds per 1,000 gallons Reagent Minimum Maximum .MgSO4.7H2O 1. 0 5.0 MIISO4.H20 0. 5 1. 5 C8.(OH)2.... 0.05 0.20

a suspension of solids in a quantity to provide about 0.3 to 1.0 pounds starch per long ton of suspended solids or preferably about 0.5 pounds. With my reagent combination added to surface drainage water, the flocculent becomes effective in the same proportions as in other water where there is no problem. Once I have added the reagents, I need not add them again as the water is reused. In fact about 20 percent new surface water can be tolerated without greatly affecting flocculation.

As a specific example to demonstrate the effectiveness of my invention, I prepared slurries of three different samples of tailings which I obtained from a magnetic taconite beneficiation operation. I used water from the St. Louis River. In each instance I added a caustic starch flocculent to the slurry in a quantity to provide 0.50 pound of starch and 025 pound NaOI-I per long ton of solids. In the first three tests I added no reagent other than the caustic starch flocculent. In the next three before adding the caustic starch, I added reagents as follows per 1000 gallons of water:

Lbs. MgSO -7H O 4.23 MnSO -H O 1.47 Ca(OH) 0.16

In the final three I recirculated water from the second three, making new slurry and adding caustic starch, but no more of the reagents. "In each instance I agitated the slurry and allowed it to settle five minutes. The results were as follows:

Fine tails Condition of Settlingrate, Suspended pH of sample supernantant feet per parts per supernatant million No treatment-control tests Reagents added as described above A Translucent 69.4 04 8.15 75.6 120 8.30 90.5 92 8.30

Treatment of recycle water,

A... Translucent..." 72.4 62 8. 00 B. d 82.8 8.00 C do 107.5 92 8.30

Indefinite.

The acceptable limit in treated water is about parts per million of solids. As the foregoing table shows, the samples treated with my combination of reagents produced supernatant liquid with a solids content Well below this limit. The first three samples showed no measurables settling rate, and the solids content was much too high.

While I have described only certain preferred ways of practicing my invention, it is apparent modifications may arise. Therefore I do not wish to be limited by the disclosure set forth, but only by the scope of the appended claims.

I claim:

1. A method of flocculating solids suspended in surface drainage water comprising adding to the water a combination of reagents which comprises: MgSO -7H O in a range of from 1.0 to 5.0 pounds per 1000' gallons of water, MnSO -H O in a range of from 0.5 to 1.5 pounds per 1000 gallons of water and Ca(OH) in a range of from 0.05 to 0.20 pounds per 1000 gallons of water and introducing to the water a caustic starch flocculent in a quantity to provide about 0.3 to 1.0 pounds of starch per long ton of suspended solids.

. 3 4 2. A method as defined in claim 1 in which the solids FOREIGN PATENTS are tailings from a magnetic taconite concentrating opera- 19 379 1899 Great Britain tlon- 481,499 3 1938 Great Britain.

R f c: a

530,946 12/1940 Great Britain.

UNITED STATES PATENTS 5 2,980,608 4/1961 Johnson 21 52 MICHAEL E. ROGERS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,414,512 December 3, 1968 Tegner A. Johnson It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 30, after "Suspended" insert solids line 31, after "per" insert hr.

Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

